US 20060290531 A1
Methods and systems are disclosed for preventing aircraft collisions with forward looking terrain avoidance (FLTA) functionality based on a terrain avoidance profile used to evaluate potential terrain threats based on the projected flight path of an aircraft in flight, and a clear terrain profile to determine whether the terrain threat has been cleared. If the terrain avoidance profile conflicts with terrain, a collision threat may exist whereby the pilot is notified and a terrain avoidance maneuver is executed. During the terrain avoidance maneuver the clear terrain profile extends in a direction substantially parallel with the horizon at or near the present altitude of the aircraft to check whether it is safe to return to the previous flight path angle or otherwise end the terrain-avoiding maneuver. When the clear terrain profile no longer conflicts with the terrain threat, a terrain clear indicator is then issued to the pilot.
1. A method for preventing controlled flight into terrain, the method comprising:
providing a first indicator to a pilot of an aircraft that a threat of potential collision with terrain exists;
providing a second indicator to the pilot of the aircraft that the threat no longer exists;
comparing a terrain avoidance profile with terrain information to determine whether the threat exists; and
comparing a clear terrain profile with the terrain information to determine whether the threat no longer exists.
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12. An apparatus for monitoring potential aircraft collision threats with terrain, the apparatus comprising:
a memory storing machine readable code; and
a processor when processing the stored machine readable code in said memory is operative to, compare an altitude and a bearing of an aircraft with terrain information to identify a potential collision threat, generate a terrain warning signal when the potential collision threat is identified, compare a forward projection of current aircraft altitude with the terrain information to identify if a terrain threat has been avoided; and generate a terrain clear signal when the terrain threat has been avoided.
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15. A system for avoiding aircraft collisions with terrain, the system comprising:
storage means for storing information relating to terrain features;
processing means for comparing a terrain avoidance profile with the information stored in said storage means, for generating an alert signal based upon said comparison if said comparison indicates a potential threat, for comparing a clear terrain profile with said information when said alert signal has been generated, and for generating a terrain clear signal when said terrain clearance profile does not conflict with said information.
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19. A method for warning a pilot of situational threats during flying, the method comprising:
determining that a terrain threat exists with reference to criteria of a first sensor; and
determining that the terrain threat has been averted with reference to criteria of a second sensor.
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This application is a continuation of and claims priority to U.S. application Ser. No. 10/326,544, filed Dec. 20, 2002, in the name of the same inventors and having the same title, all of which is incorporated herein by reference.
1. Field of the Invention
The present invention generally relates to methods and systems for preventing collisions between aircraft and terrain. More particularly, the present invention defines terrain warning systems and methods that inform a pilot to avoid collision with terrain and when hazardous terrain has been traversed.
2. Background of the Invention
Ground Proximity Warning Systems (GPWS), Ground Collision Avoidance Systems (GCAS) and/or Terrain Awareness and Warning Systems (TAWS), are used in aircraft to inform pilots or other flight crewmembers of likely or imminent collision with terrain. For simplicity, these and other system for warning pilots of potential collision with terrain are collectively and individually referred to herein as TAWS. TSO-C151a (Technical Standard Order), which is fully incorporated herein by reference including its Appendices, and RTCA DO-161A, prescribe minimum operational performance standards for TAWS equipment in the United States.
TAWS includes a Forward Looking Terrain Avoidance (FLTA) function which looks ahead of an aircraft along and below the aircraft's lateral and vertical flight path and provides alerts to a flight crew if a potential Controlled Flight Into Terrain (CFIT) threat exists. CFIT is an aircraft accident where a completely airworthy aircraft is inadvertently flown into terrain (which may include man-made obstacles) or water. In the United States, Class A TAWS equipment must provide terrain information on a display system such as a weather radar display or other video output device. In such a system, visual and aural signals are provided to a flight crew for both caution and warning alerts in one or more of the following situations:
A “caution alert” as used herein is provided when a potentially hazardous flight condition is encountered, immediate crew/pilot attention is required, and a potential for crew/pilot action exists. In a TAWS, a typically caution alert is in the form of an audible notification of a flight condition, e.g., “terrain ahead” and/or corresponding visual indicators of the flight condition such as an amber or yellow light on a display. A “warning alert” as used herein is provided when a potentially hazardous flight condition is encountered and immediate crew/pilot action is required to avoid a hazardous flight condition. Typically, a warning alert may be in the form of an audible instruction to take action (e.g., “terrain, terrain; pull up, pull up”) and/or corresponding visual indicator (e.g., a red light or symbol on a cockpit display) notifying a crew or pilot that action is required to avoid an imminent threat. In most instances a warning alert is only provided after a caution alert is provided. The differences between these alert types are made primarily to distinguish between severities of threats from terrain that one may encounter during flight.
Forward Looking Terrain Avoidance (FLTA) in TAWS uses a “look ahead” or “sensor” profile for determining when to generate terrain caution and/or warning alerts. These sensor profiles typically include a projection of the aircraft's future position using two or more segments including a response segment, which projects the flight path of the aircraft a certain length of time in front of an aircraft, and a climb profile, which projects an angle of increasing elevation that the aircraft might take to avoid terrain. In a spatial sense, the climb profile is connected at the forward end of the response segment. This look ahead profile is compared with terrain data to determine whether an aircraft is encountering a terrain threat. If terrain data intersects the TAWS look ahead profile, then a caution or warning alert is given to the flight crew depending on the severity of the threat. The primary difference between generation of a caution alert and a warning alert is the length of the response segment in a look ahead profile. That is, an increased length of time is used for a caution alert, whereas a smaller length of time for response is used for a warning alert.
The climb profile is a prediction of the change in aircraft altitude for overcoming terrain threats and is based, at least in part, on an aircraft climb angle. A “climb angle” is the angle of a flight path measured from the horizon.
Fixed profiles used in some conventional FLTA processing may not take into account the actual climb angle obtainable by a particular aircraft, but rather utilize a fixed, conservative climb angle that is presumed to be safe for all types of aircraft that may utilize a TAWS. Accordingly, some conventional sensor profiles are static by nature and do not account for certain differences between types of aircraft or take into account actual performance characteristics of the aircraft in which the TAWS is present. Variances between, for example, thrust or aerodynamic characteristics and performance of aircraft can significantly alter the true climb angle that may be utilized by an aircraft for escaping a terrain collision threat. Consequently the true climb angle of a particular aircraft may not match the predicted climb profile used with conventional FLTA.
The conventional approach, using a fixed climb profile, has a drawback that the climb profile may not be suitable for all aircraft. For example, if an aircraft is unable to attain a climb angle predicted in the look ahead profile, then the aircraft may not be able to sufficiently avoid a terrain threat when a warning alert is sounded. Alternatively, if the climb profile is too conservative for the actual climb angle obtainable by an aircraft, alerts may be generated before any respective caution or warning alert is necessary or desired. These unnecessary alerts are referred to as “nuisance alerts,” and are generally desired to be minimized. For the foregoing reasons, it is desirable to provide a terrain avoidance profile that considers the specifications and recently demonstrated characteristics of the aircraft for which it is used.
Referring now to
This conventional approach to TAWS suffers from one or more of the following problems. When visual inspection by a pilot is impossible or impaired, e.g., when flying in fog, darkness, or other visual impairment condition, a pilot of aircraft 10 may be entirely surprised by a terrain warning alert. Since the terrain warning alert provides no indicia of how fast to “pull up” or how much to “pull up,” the pilot will most likely enact the most rigorous increase in elevation possible. Moreover, because aural alert 25 continues to sound until aircraft 10 reaches an elevation safe enough to clear terrain 50, the pilot will continue the most rigorous increase in elevation possible until the terrain is cleared. This type of extreme avoidance maneuver can: (i) induce aircraft 10 to stall, thereby increasing the chance of collision with the terrain, (ii) lead to injury of passengers, flight crew or cargo or at least an uncomfortable ride due to severe course alterations, and/or (iii) cause unnecessary stress on the pilot and/or damage to aircraft 10. With the conventional methods and systems, a pilot may not realize danger has subsided until the aural alert ceases, even though in reality, a timely response by the pilot and a slight or gradual increase in altitude might avoid collision.
Thus, a need exists for systems and methods, which overcome these and other problems.
In accordance with an embodiment of the invention, a method is disclosed for preventing controlled flight into terrain, the method comprising providing a first indicator to a pilot of an aircraft that a threat of potential collision with terrain exists, providing a second indicator to the pilot of the aircraft that the threat no longer exists, comparing a terrain avoidance profile with terrain information to determine whether the threat exists, and comparing a clear terrain profile with the terrain information to determine whether the threat no longer exists.
In accordance with another embodiment of the invention, an apparatus is disclosed for monitoring potential aircraft collision threats with terrain, the apparatus comprising a memory storing machine readable code; and a processor when processing the stored machine readable code in the memory is operative to, compare an altitude and a bearing of an aircraft with terrain information to identify a potential collision threat, generate a terrain warning signal when the potential collision threat is identified, compare a forward projection of current aircraft altitude with the terrain information to identify if a terrain threat has been avoided, and generate a terrain clear signal when the terrain threat has been avoided.
In accordance with yet another embodiment of the invention, a system is disclosed for avoiding aircraft collisions with terrain, the system comprising storage means for storing information relating to terrain features; processing means for comparing a terrain avoidance profile with the information stored in the storage means, for generating an alert signal based upon the comparison if the comparison indicates a potential threat, for comparing a clear terrain profile with the information when the alert signal has been generated, and for generating a terrain clear signal when the terrain clearance profile does not conflict with the information.
In accordance with still another embodiment of the invention, a method is disclosed for warning a pilot of situational threats during flying, the method comprising determining that a terrain threat exists with reference to criteria of a first sensor, and determining that the terrain threat has been averted with reference to criteria of a second sensor.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.
Reference will now be made in detail to the present exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
When a terrain alert has been issued and ceases due to a pilot initiating a terrain avoiding maneuver, the improved system having modified FLTA of the present invention will utilize a second sensor profile 155, in addition to sensor profile 150, to determine whether the pilot of aircraft 100 should maintain the terrain avoiding maneuver (for example, whether the aircraft may cease deviating from its original flight path or increasing in altitude). This second profile 155 is referred to herein as a “clear terrain profile.” According to one embodiment of the invention clear terrain profile 155 extends in a substantially horizontal direction regardless of the climb angle of aircraft 100.
During a terrain avoidance maneuver, e.g., aircraft 100 at position (C), if clear terrain profile 155 conflicts with the terrain 50, the pilot of aircraft 100 will not be informed that the terrain has been cleared or that the terrain threat has ended. In a modified embodiment of the invention, the pilot or flight crew may be instructed to maintain the terrain-avoiding maneuver (for example, the current climb angle or banking maneuver) using an aural and/or visual indicator. Alternatively, if appropriate, the alert may change from a “warning alert” to a “caution alert” as those terms are defined in TSO-C151a.
When aircraft 100 exceeds the altitude of the terrain 50, plus preferably a minimum safe clearance altitude, clear terrain profile 155 no longer conflicts with terrain 50 and the pilot is notified that the terrain threat has been overcome. This notification may be provided using any form of audio and/or visual indicia that informs the pilot that the potential terrain collision threat has ended. In one aspect of the invention an aural alert, for example, “Terrain Clear,” “Clear of Terrain,” “End Terrain Threat” or other similar audible indicator would effectively inform the pilot that it is safe to end the terrain avoidance maneuver (e.g., level off). Preferably, although not mandatory, clear terrain profile 155 includes a built in safety margin of altitude to prevent aircraft 100 from leveling off immediately after surpassing the altitude of terrain 50. Such built in safety margin is discretionary and might be, for example, five hundred feet above any threatening terrain feature or a variable threshold depending on phase of flight or proximity to the nearest airport.
Minimum clearance segment 151 may be included as part of terrain avoidance profile 150 to serve the purpose of providing a minimum safety margin of altitude for safe flight over terrain or Minimum Terrain Clearance Distance (MTCD). Minimum clearance segment 151 may be set for a fixed minimum clearance altitude, e.g., five-hundred feet or be a variable threshold based upon the phase of aircraft flight.
Pilot response segment 152 projects the aircraft's trajectory for a specified amount of time prior to a pilot taking action in response to an alert. Segment 152 essentially projects in the direction of the aircraft's current flight path angle, for a length of time T1. The length of time T1 for pilot response may vary depending on the type of warning involved, e.g., caution or warning, requirements from various airworthiness authorities and/or at the discretion of the party responsible for the aircraft, e.g., commercial airline, etc. In certain preferred embodiments, T1 is twenty seconds for a caution alert and eight seconds for a warning alert.
Aircraft maneuver segment 153 is a model of the pull up behavior of an aircraft in responding to an alert. The length of time T2 for segment 153 may vary based on the theoretical climb vertical speed of an aircraft (Vt), the current vertical speed of the aircraft (Vp) and an assumed acceleration relative to gravity, e.g., 0.5 g as follows:
Climb segment 154 is a model of the predicted climb capability of an aircraft. Essentially segment 154 is a straight segment reflecting the climb angle that may be achieved by an aircraft. Segment 154 has a length of time T3 which may be based on relevant TAWS regulations and requirements. In certain embodiments T3 is one hundred and twelve seconds and may be modified in certain cases depending on, for example, the various CFIT situations discussed previously.
Times T1, T2 and T3 for respective segments in profile 150 are not limited to the specific times or formulas set forth above and consequently, times T1, T2 and/or T3 may be selected or adjusted as desired or set as required by pertinent airworthiness authority requirements or government regulations.
The climb angle for segment 154 is typically set conservatively compared to an expected climb gradient based on performance models of a particular aircraft, for example, ninety percent of the calculated climb gradient. Maneuver segment 153 and climb segment 154 may be modeled after any aircraft's climb maneuver and achievable escape angle used to avoid a terrain threat.
By way of example, segments 153 and 154 may be: (i) fixed (e.g., a fixed six degree climb angle); (ii) based on the published maneuver and climb performance models for a particular aircraft; and/or, to reduce the number of nuisance alerts, preferably (iii) based on published performance models and adjusted using current and/or recently demonstrated flight performance characteristics of the aircraft. Actual aircraft performance characteristics used for calculating a climb gradient profile might include, for example, current aircraft weight (including remaining fuel and/or weapons payload), current ground and/or vertical speeds, thrust, temperature, wind shear, and/or other factors known to affect climb performance and climb angle of an aircraft. Nuisance alerts will be reduced when maneuver segment 153 and climb segment 154 are modeled after actual climb capabilities of an aircraft.
In other embodiments of the present invention, degradations in aircraft performance may be considered in calculating a look ahead profile. For example, by taking into account known deficiencies in an aircraft's performance, such as reductions in engine thrust output as compared to published performance specifications, the climb profile may be adjusted to reflect actual climb capabilities. Consequently, an increased safety margin for an aircraft to avoid terrain may be achieved while at the same time reducing the number of nuisance alerts generated by a TAWS.
Terrain check segment 155B serves the purpose of determining whether a terrain threat is still present during a terrain avoidance maneuver (e.g., pull-up or banking maneuver). Segment 155B preferably extends substantially in a horizontal direction regardless of the climb angle or flight path angle of the aircraft. The length of segment 155B is also discretionary and may be fixed or variable as a function of time, ground speed or other factors. Example shapes and sizes of profiles 150 and 155 are depicted in the appended drawing (
Minimum clearance segment 151 (
However, if the pilot maneuvers the aircraft so that any conflict between the projected flight path and any terrain feature is resolved 540 (for example, as determined by the terrain avoidance profile no longer intersecting the terrain data model), then the terrain alert may cease or be modified to a lower threat mode. This however, does not necessarily mean that the terrain threat has been traversed, but only that, on its current flight path angle, imminent collision with the terrain no longer exists. During vertical maneuvering to avoid the terrain threat, the altitude of terrain in the immediate track of the aircraft (Talt) is compared with the altitude of the aircraft at its current position (Aalt) (e.g., using clear terrain profile 155 (
When Aalt exceeds Talt (preferably plus a minimum allowed terrain clearance, e.g., five hundred feet above Talt) the pilot is informed that the terrain threat has been cleared 560 using any appropriate aural or visual indicia. When the terrain clear indicator or indicia are provided, the pilot will know that it is safe to level the aircraft from its terrain-avoiding ascent.
As mentioned previously, there are several possible types of calculations for including the minimum terrain clearance distance (MTCD), for example, in addition to that shown, Aalt>Talt+buffer, or Aalt−Talt>buffer. Accordingly, method 500 is not limited to any particular algorithm.
Terrain information source 610, flight data source 620, and optional, aircraft performance database 670 provide the information and data inputs 602 for operation of system 600. Terrain processing device 630 and memory 640 from processing system 605 that utilizes information from inputs 602 for comparing and/or storing the terrain avoidance and clear terrain profiles with modeled terrain features and generating alerts.
Terrain information source 610 provides information to processing device 630 regarding coordinates and altitudes of naturally occurring terrain and man-made obstacles, collectively referred to herein as “terrain”. Terrain information source 610 may be any single device or combination of devices for accomplishing this end including, for example, a database comprising a model of terrain stored in a memory or receiver obtaining information regarding surrounding terrain over a wireless communications link such as a transponder.
Flight data source 620 functions to provide information to processing device 630 regarding current flight information such as altitude, bearing, ground speed, and vertical speed. Flight data source 620 may be any single device or combination of devices for serving this purpose including, for example, one or more altimeters, a global positioning receiver, a gyroscope, air data computer, a traffic collision and avoidance system (TCAS) and the like.
Processing device 630 serves to compare flight and terrain data from sources 610, 620 and optionally database 670 and generate output information to inform a pilot of potential terrain threats. The terrain avoidance profile 150 (
Memory 640 stores machine-readable code to be executed by processing device 630. Memory 640 may function as a Random Access Memory, Read Only Memory, storage buffer or other memory function for storing control settings, temporary information, constants, equations or other information necessary for processing the information and generating alert signals as described herein. Memory 640 may be a single device or combination of devices for accomplishing this purpose and may be integrated or partially integrated with processing device 630. Memory 640 may be a fixed memory or portable memory and may even serve as terrain information source 610, e.g., a terrain database stored in a physical memory device or conduit for flight data information.
Output devices 652 and 654 serve the purpose of providing information about terrain to a pilot and function to convert electrical signals generated by processing device 630 and/or other devices into light or sound. Any single device or combination of devices that accomplish this function can be used, for example, a transducer, an analog display, a digital display, an L.E.D., and/or a laser. In a preferred embodiment, an analog speaker is used for outputting aural indicia and a display device such as a cockpit display or other electronic flight instrument system display may be used to output visual indicia.
System 600 may be an integrated device, discreet components of a shared system, or other type of processing configuration able to perform the functions described herein. System 600 calculates, if not fixed values, the terrain avoidance profile and clear terrain profile of the types previously discussed, and compares the profiles with values obtained from terrain information source 610 to generate caution alerts, warning alerts, clear terrain indicia as previously discussed. In a preferred embodiment, a terrain avoidance profile (e.g. profile 150 in
Since conventional TAWS also utilize a processor and software for comparing conventional terrain avoidance profiles with terrain information, modifying these systems to perform in accordance with minimum aspects of the present invention can be accomplished by updating terrain avoidance software.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.